A deformed layer is formed on a surface of a metal mechanically machined through methods such as cutting, grinding, polishing, etc., as a result of the mechanical machining. The deformed layer formed on the metal surface is a metal oxide layer formed by heat generated at the time of cutting or grinding process, which is a finish surface layer having different characteristics from a metal basic material. The deformed layer causes plastic deformation, work hardening, work softening, residual stress, etc., having largely adverse effects on properties such as abrasion resistance, etc., of the metal, which deteriorates resistance to damage of the metal surface, and causes refinement of crystal grain, re-crystallization and crack, etc. Accordingly, a surface-treatment method for removing the deformed layer of the metal is necessarily required so as not to cause these problems.
The surface-treatment method for removing the deformed layer formed on a metal surface layer to minimize metal damage includes laser etching, etc. The laser etching is one of the methods generally used in technology for implementing fine patterns on the metal surface, which has been actively used since the metal surface is capable of being finely processed by irradiating a laser beam to the metal, thereby finely removing the deformed layer which is thinly formed on the metal surface.
However, since a pulse intensity of the laser beam irradiated by the laser etching is excessively high, the metal basic material as well as the deformed layer of the metal surface layer are affected by the laser beam and heat caused by the beam, such that the metal is damaged, and the deformed layer is formed again on the surface of damaged metal basic material, etc., which causes a problem in that efficiency is reduced in the removing process of the deformed layer of the metal. Therefore, it is demanded to develop a method for effectively removing the deformed layer on the metal surface capable of solving these problems.